US5884162A - 1×N communication system for private branch exchange - Google Patents

1×N communication system for private branch exchange Download PDF

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Publication number
US5884162A
US5884162A US07/910,219 US91021992A US5884162A US 5884162 A US5884162 A US 5884162A US 91021992 A US91021992 A US 91021992A US 5884162 A US5884162 A US 5884162A
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Prior art keywords
press
talk
terminals
signals
signal
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Expired - Fee Related
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US07/910,219
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English (en)
Inventor
Shigeru Yamazaki
Akihiko Hiramatu
Kazuo Seko
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Priority claimed from JP19504491A external-priority patent/JPH0522190A/ja
Priority claimed from JP3234312A external-priority patent/JP2743651B2/ja
Application filed by Mitsubishi Electric Corp filed Critical Mitsubishi Electric Corp
Assigned to MITSUBISHI DENKI KABUSHIKI KAISHA reassignment MITSUBISHI DENKI KABUSHIKI KAISHA ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: HIRAMATU, AKIHIKO, SEKO, KAZUO, YAMAZAKI, SHIGERU
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04—Large scale networks; Deep hierarchical networks
    • H04W84/08—Trunked mobile radio systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13003—Constructional details of switching devices
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13058—Interrupt request
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13098—Mobile subscriber
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13106—Microprocessor, CPU
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13194—Four wire connection, transmission
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/1322—PBX
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13292—Time division multiplexing, TDM
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/1334—Configuration within the switch

Definitions

  • This invention relates to a communication system enabling N people to use a switching system such as a private branch exchange for 1 ⁇ N communication (N being an integer greater than two).
  • the modern private branch exchange is a digital electronic device comprising a time-division switch and a central controller.
  • the central controller can be programmed to implement a variety of services besides what is technically referred to as "plain old telephone service" (POTS).
  • POTS plain old telephone service
  • One of these additional services is a 1 ⁇ N communication service known, for example, as announcement or broadcast service. This service can be utilized for communication among employees of a department store, hotel, hospital, or other organization.
  • a prior-art 1 ⁇ N communication scheme employs standard extension telephone sets coupled to a private branch exchange, either by wires or by wireless links.
  • Information designating N of these extension telephone sets as a broadcast group is stored in a memory of the central controller.
  • the central controller responds by setting up a circuit in the private branch exchange that allows the person's voice to be heard at the rest of the N extension telephone sets in the group.
  • the person performs another special operation to release the circuit. If another person at one of the N extension telephone sets wants to reply to the announcement, he can do so by a similar series of operations.
  • Another object of the invention is to provide 1 ⁇ N communication without requiring a central controller to execute a special service program.
  • Still another object is to provide 1 ⁇ N communication without requiring extensive wiring.
  • Yet another object is to enable a 1 ⁇ N communication system to be expanded flexibly.
  • the invented 1 ⁇ N communication comprises at least three voice terminals equipped with press-talk switches for generating press-talk signals, a switching system for switching communication paths among these terminals, a central controller for controlling the switching system, and a press-talk trunk that receives the press-talk signals from the terminals.
  • the central controller scans the press-talk trunk. When it finds an active press-talk signal, the central controller sets up a 1 ⁇ N communication path in the switching system enabling the person who operated the press-talk switch that generated the active press-talk signal to speak to people at the other terminals. If more than one press-talk signal is active, the central controller selects a single press-talk signal.
  • the press-talk trunk itself detects and selects an active press-talk signal and notifies the central controller.
  • the central controller sets up a 1 ⁇ N communication path in the switching system.
  • the press-talk trunk also receives voice signals from all the terminals, selects a voice signal from a terminal having an active press-talk signal, and sends that voice signal back to all the other terminals.
  • press-talk trunks are cascaded.
  • Each press-talk trunk receives press-talk signals and voice signals.
  • a press-talk trunk selects a single active press talk signal and the corresponding voice signal.
  • Signals selected by a lower-order press-talk trunk are input to a higher-order press-talk trunk.
  • FIG. 1 illustrates a first novel 1 ⁇ N communication system.
  • FIG. 2 illustrates a second novel 1 ⁇ N communication system.
  • FIG. 3 is a more detailed drawing of the press-talk trunk in FIG. 2.
  • FIG. 3 illustrates a third novel 1 ⁇ N communication system.
  • FIG. 5 is a more detailed drawing of the press-talk trunk in FIG. 4.
  • FIG. 6 illustrates the cascading of press-talk trunks.
  • FIG. 7 illustrates the cascading of press-talk trunks via a wireless link.
  • a first novel 1 ⁇ N communication system comprises a private branch exchange 2 and a plurality of terminals 4.
  • the terminals 4 are installed, for example, at employee stations in a hotel, and are coupled to the private branch exchange 2 by wire pairs 5 for carrying analog voice signals. Although shown by a single line in the drawings, each wire pair 5 comprises two wires.
  • the terminals 4 are also coupled to a press-talk trunk 6 in the private branch exchange 2 by press-talk wires 7 for carrying press-talk signals.
  • the press-talk signal is in this case a simple on-off signal.
  • the terminals 4 are extension telephone sets having the usual handset and dial push buttons (or a rotary dial), and an additional press-talk pushbutton 9 labeled with, for example, the words "Press to Talk.”
  • the handset has a built-in microphone and speaker.
  • Each terminal 4 preferably also has an external speaker that can operate even when the handset is on-hook.
  • the press-talk pushbutton 9 functions as a contact switch to produce the press-talk signal mentioned previously.
  • the press-talk signal is active (on) when the press-talk pushbutton 9 is depressed and inactive (off) when the press-talk pushbutton 9 is not depressed.
  • the invention is not limited to the type of press-talk pushbutton just described.
  • the press-talk pushbutton may operate as a toggle control, in which case the press-talk signal changes between the active and inactive states each time the press-talk pushbutton is pressed.
  • the invention can also be practiced using press-talk lever switches or other types of press-talk switches instead of pushbuttons.
  • the private branch exchange 2 is coupled not only to the terminals 4 but also to standard extension telephone sets not equipped with press-talk pushbuttons, and to one or more external lines for communication with a public telephone network.
  • Standard extension telephone sets are installed, for example, in hotel guest rooms.
  • the standard extension telephone sets and external lines are omitted from the drawings to avoid obscuring the invention with unnecessary detail.
  • the private branch exchange 2 has a time-division switch 10 that is coupled to and controlled by a central controller 12.
  • the central controller 12 is also coupled via a control bus 13 to the press-talk trunk 6.
  • the private branch exchange 2 further comprises a plurality of line cards 14 to which the wire pairs 5 are connected, and a plurality of four-wire internal highways 16 via which the line cards 14 are coupled to the time-division switch 10.
  • the internal highways 16 carry digital signals in assigned time slots. Time-division switches, central controllers, line cards, and four-wire highways are well known, so the following description will be brief.
  • the time-division switch 10 is a switching system that establishes communication paths among the terminals 4 and other standard extension telephone sets, or between a terminal 4 or standard extension telephone set and an external telephone line. These paths are established by assigning and interchanging time slots.
  • the central controller 12 is a digital computing device that executes programs for setting up and clearing communication paths in the time-division switch 10.
  • the line cards 14 are interfaces between the terminals 4 and the private branch exchange 2; each comprises an analog-to-digital and digital-to-analog converter 18 and a two-wire/four-wire converter 20. These line cards 14 are identical to line cards (not shown) used for coupling the private branch exchange 2 to standard extension telephone sets.
  • the private branch exchange 2 is configured as a mainframe with slots for installing line cards 14 and the press-talk trunk 6.
  • the press-talk trunk 6 is in this case an extremely simple device comprising a plurality of I/O ports to which the press-talk wires 7 are coupled.
  • Each I/O port outputs, for example, the logic value zero when the incoming press-talk signal is active, and the logic value one when the incoming press-talk signal is inactive.
  • the control controller 12 rapidly and repeatedly scans the I/O ports in the press-talk trunk 6 by addressing them and reading their values in a cyclic manner. When it detects a logic zero at an I/O port, in this case the I/O port corresponding to the uppermost terminal 4, the central controller 12 sets up the voice communication path shown in the drawing in the time-division switch 10, linking the microphone at the uppermost terminal 4 to speakers (preferably external speakers) at the other terminals 4. The person at the uppermost terminal 4 in the drawing can then speak to people at the other terminals 4.
  • the central controller 12 When he has finished speaking, the person at the uppermost terminal 4 releases the press-talk pushbutton 9. In scanning the I/O ports of the press-talk trunk 6, the central controller 12 now finds that the press-talk signal from the uppermost terminal 4 is inactive, so it clears the voice communication path shown in FIG. 1. After this, if someone at another terminal 4 wishes to speak, he can do so by pressing his own press-talk pushbutton 9.
  • the central controller 12 is programmed to accept only one active press-talk signal at a time. For example, after detecting a logic zero at an I/O port, the central controller 12 scans only that I/O port until that port reverts to the logic-one state. The central controller is also programmed to exclude from the 1 ⁇ N communication path any terminals 4 that are currently making ordinary (1 ⁇ 1) telephone calls.
  • An advantage of the system in FIG. 1 is that it does not require any complex or difficult operations such as entry of a service code.
  • a person who wishes to speak simply picks up the handset at his terminal 4, depresses the press-talk button 9, and starts talking.
  • FIG. 2 shows a second novel 1 ⁇ N communication system that accommodates both wired and wireless terminals.
  • the private branch exchange 2, terminals 4, time-division switch 10, central controller 12, line cards 14, and internal highways 16 in FIG. 2 are generally similar to the elements with the same reference numerals in FIG. 1. Detailed descriptions will therefore be omitted, except to note that the line cards 14 are coupled to the time-division switch 10 not only by internal highways 16 but also by press-talk highways 21 which transmit press-talk signals from the terminals 4.
  • the press-talk signals transmitted on these press-talk highways 21 are digital signals.
  • the press-talk highways 21 are four-wire highways with separate paths for incoming and outgoing signals. Besides press-talk signals, the press-talk highways 21 carry other signaling information such as identification codes identifying the terminals 4.
  • the system in FIG. 2 has a plurality of fixed base stations 22 installed at appropriate locations.
  • a hotel for example, may have one fixed base station 22 on each floor.
  • Each fixed base station 22 has a transmitter, receiver, antenna, multiplexer, demultiplexer, and other standard components of base stations in wireless communication systems.
  • the fixed base stations 22 are linked to the time-division switch 10 by four-wire internal highways 16 and four-wire press-talk highways 21.
  • the system in FIG. 2 has portable wireless terminals 24.
  • wireless terminals 24 might be assigned to individual employees, to be worn or kept at hand while the employee is on duty.
  • Each wireless terminal 24 is generally similar to a standard cordless telephone set, having a microphone, speaker, antenna, and battery power supply. Some or all of the wireless terminals 24 may have dial pushbuttons for making ordinary telephone calls.
  • Each wireless terminal 24 has a press-talk pushbutton 9.
  • the wireless terminals 24 communicate with the fixed base stations 22 by means of wireless signals transmitted between their antennas. Although the two fixed base stations 22 in FIG. 2 are shown communicating with only one wireless terminal 24 apiece, a fixed base station 22 is capable of communicating simultaneously with a plurality of wireless terminals 24, using a different channel for each. Channels are assigned to wireless terminals 24 in the area served by a fixed base station 22, and calls are handed off when a wireless terminal 24 is carried from the area served by one fixed base station 22 to the area served by another fixed base station 22. Details of these processes will be omitted since they are well known.
  • the wireless links between the fixed base stations 22 and wireless terminals 24 may be digital or analog.
  • the invention is not restricted to any particular wireless communication technology.
  • the fixed base stations 22 can also communicate with standard cordless telephone sets, not shown in the drawing, which have dial pushbuttons but no press-talk pushbutton 9.
  • each fixed base station 22 Since each fixed base station 22 has a plurality of channels, it multiplexes signals arriving on different channels form the wireless terminals 24 into a single signal sent on the internal highway 16, and demultiplexes signals from the internal highway 16 to different outgoing channels to the wireless terminals 24. Details of these processes will also be omitted; suffice it to say that different channels are assigned to different time slots on the internal highways 16.
  • the press-talk highways 21 are similarly multiplexed.
  • the multiplexed press-talk signals from all the line cards 14 and fixed based stations 22 are sent via another press-talk highway 28 to press-talk trunk 30.
  • Returning signals from the press-talk trunk 30 are sent to the line cards 14 and fixed base stations 22 via the press-talk highways 28 and 21.
  • a multiplexer-demultiplexer 32 demultiplexes the signals from the press-talk highway 28 and sends them to a discriminator 34.
  • the discriminator 34 When an active press-talk signal arrives, the discriminator 34 notifies the central controller 12 in the private branch exchange 2 by generating an interrupt signal (INT).
  • INT interrupt signal
  • the discriminator 34 selects the one that arrived first and notifies the central controller 12 of that signal only.
  • FIG. 3 is a more detailed drawing of the press-talk trunk 30 in FIG. 2, showing one way in which the signal interface can be implemented.
  • the press-talk highway 28 carries data at an aggregate rate of, for example, 2.048 megabits per second. A total of, for example, thirty-two channels are multiplexed into this press-talk highway 28, each channel having a data rate of sixty-four kilobits per second. The channels are assigned to eight-bit time slots.
  • the multiplexer-demultiplexer 32 demultiplexes incoming data to thirty-two separate signal channels (CH1, CH2, CH3, . . . in the drawing), each having a data rate of sixty-four kilobits per second. Every 0.125 milliseconds, the discriminator 34 receives eight bits of data from each channel. The first of these eight bits is a press-talk flag that has the value zero to indicate depression of the press-talk pushbutton 9 at the corresponding terminal 4 or wireless terminal 24, or the value one to indicate that the press-talk pushbutton 9 is not depressed. The other seven bits are, for example, an identification (ID) code of the terminal 4 or wireless terminal 24 using the channel.
  • ID identification
  • the discriminator 34 processes the incoming data and returns an eight-bit code to each of the thirty-two channels.
  • the first bit in this return code is a busy/free flag indicating whether 1 ⁇ N communication is currently in progress. This bit has the value zero when a press-talk pushbutton 9 at one of the terminals 4 or wireless terminals 24 is depressed, and the value one when none of the press-talk pushbuttons 9 is depressed.
  • the second bit in the return code is a clear-to-talk flag indicating whether this specific channel has been selected by the discriminator 34, enabling the person at the corresponding terminal 4 or wireless terminal 24 to talk to people at other terminals.
  • the other six bits are, for example, identification code bits of the terminal 4 or wireless terminal 24 selected by the discriminator 34.
  • the multiplexer-demultiplexer 32 multiplexes the thirty-two channels of data received from the discriminator 34 and sends the resulting multiplexed signal to the press-talk highway 28 at the rate of 2.048 megabits per second.
  • the paths indicated by dotted arrows in the time-division switch 10, linking the press-talk highways 21 to the press-talk highway 28, are set up when the system is installed and are left permanently connected.
  • the discriminator 34 accordingly always knows which press-talk pushbuttons 9 are depressed.
  • this wireless terminal 24 When its press-talk pushbutton 9 is depressed, this wireless terminal 24 begins in transmitting a carrier signal to the fixed base station 22 in the top left. If the wireless terminal 24 is also equipped with dial pushbuttons for making ordinary telephone calls, the transmitted signal includes information indicating specifically that the press-talk pushbutton 9 was pressed, rather than a pushbutton for making an ordinary call. If the wireless terminal 24 is not equipped for making ordinary telephone calls and the fixed base station 22 can recognize this from the identification code of the wireless terminal 24, then specific press-talk information may be unnecessary, presence of the carrier signal sufficing to indicate that the press-talk pushbutton 9 is depressed. In any case, the fixed base station 22 sends an active press-talk signal to the press-talk trunk 30 by clearing the press-talk flag indicated in FIG. 3 to zero.
  • the discriminator 34 detects this active press-talk signal. If 1 ⁇ N communication is already in progress, the discriminator 34 sends return information to that effect; i.e. it sets the clear-to-talk flag in FIG. 3 to one and the busy/free flag to zero. If 1 ⁇ N communication is not in progress, the discriminator 34 changes the 1 ⁇ N communication status to in-progress, sends a return code in which the busy/free and clear-to-talk flags both have the value zero, and sends an interrupt signal to the central controller 12. The discriminator 34 also notifies the central controller 12 of the specific channel on which the press-talk pushbutton 9 has been pressed. The central controller 12 executes an interrupt-handling routine that sets up the voice path indicated by solid arrows in FIG. 2 in the time-division switch 10, enabling the voice of the person at the wireless terminal 24 in the top left to be heard by people at other wireless terminals 24 and terminals 4.
  • the system in FIG. 2 has the advantage that a person who wants to speak only has to press a single pushbutton.
  • Another advantage of the system in FIG. 2 is easy installation, because the press-talk trunk 30 is connected only to the private branch exchange 2.
  • the central controller 12 does not have to detect a service code as in the prior art or scan the press-talk trunk as in FIG. 1; it only has to respond to an interrupt signal.
  • the information contained in the eight-bit time slots in FIG. 3 can be used to provide service features such as the following.
  • the identification code in an incoming time slot may specify a service priority class.
  • the discriminator 34 can interrupt a 1 ⁇ N call from a lower-priority terminal to permit a call to be made from a higher-priority terminal.
  • the busy/free flags in the outgoing time slots can be used to switch on external speakers at the terminals 4, turn up the volume of the speakers built into the wireless terminals 24, or light an indicator lamp or sound an alerting tone at these terminals.
  • the clear-to-talk flags in the outgoing time slots can be used to control indicator lamps at the terminals 4 and the wireless terminals 24, so that a person who has pressed a press-talk pushbutton 9 can confirm that he is clear to talk.
  • the identification code in the outgoing time slots may indicate the priority of the current speaker's terminal. This enables urgent 1 ⁇ N calls or calls from the higher-priority terminals to be announced or indicated by an alarm tone, flashing lamp, or other means at the called terminals.
  • FIG. 4 shows a third novel 1 ⁇ N communication system.
  • this system all switching of 1 ⁇ N communication is carried out in the press-talk trunk 36.
  • Components other than the press-talk trunk 36 are the same as the components with the same reference numerals in FIG. 2, so descriptions will be omitted.
  • FIG. 5 shows the structure and interconnections of the press-talk trunk 36 in more detail.
  • the press-talk trunk 36 is coupled to the time-division switch 10 by an internal highway 16 and a press-talk highway 28.
  • the press-talk highway 28 terminates at a multiplexer-demultiplexer 32 which is coupled to a discriminator 34; this part of the press-talk trunk 36 is the same as in FIGS. 2 and 3.
  • the internal highway 16 terminates at a multiplexer-demultiplexer 37, basically identical to the multiplexer-demultiplexer 32, which couples the internal highway 16 to a selector 38.
  • the multiplexer-demultiplexer 32 and multiplexer-demultiplexer 37 in FIG. 5 are shown as demultiplexing the incoming signal to only four channels, but the actual number of channels may of course be larger, such as the thirty-two channels shown in FIG. 3.
  • the invention is not restricted to any particular number of channels.
  • the selector 38 selects one of the incoming channels demultiplexes by the multiplexer-demultiplexer 37 and connects it to all of the outgoing channels to be multiplexed by the multiplexer-demultiplexer 37.
  • the selector 38 is controlled by a signal from the discriminator 34.
  • the operation of the system in FIGS. 4 and 5 is identical to the operation of the system in FIGS. 2 and 3 except that when the press-talk pushbutton 9 is pressed at a terminal 4 or wireless terminal 24, instead of sending an interrupt signal to the central controller 12, the discriminator 34 in the press-talk trunk 36 causes the selector 38 to select the corresponding channel, thereby enabling the person who depressed the press-talk pushbutton 9 to speak to people at the other terminals 4 and wireless terminals 24. When the person releases the press-talk button 9, the discriminator 34 sets the selector 38 to a neutral state in which none of the incoming channels from the multiplexer-demultiplexer 37 is selected.
  • the voice signal selected by the selector 38 returns to the terminal from which it originated, as well as to other terminals. If this feature is not desired, the selector 38 can be provided with additional means for canceling the return path to the terminal of origin.
  • the system shown in FIGS. 4 and 5 has the advantage of implementing 1 ⁇ N communication with no intervention by the central controller 12. Accordingly, 1 ⁇ N communication imposes no load on the central controller 12.
  • the 1 ⁇ N communication system is moreover not restricted by the processing capability of the central controller 12, making it possible to accommodate a large number of terminals 4 and wireless terminals 24.
  • press-talk trunks can be cascaded as described next.
  • the time-division switch and multiplexing apparatus will be omitted and the press-talk and voice signals from the terminals will be shown as supplied directly to the press-talk trunks, but the cascading scheme can also be used when press-talk signals and voice signals are routed through the time-division switch as in FIG. 4.
  • terminals 4 with press-talk pushbuttons 9 are coupled to two press-talk trunks, a master press-talk trunk 40 and a slave press-talk trunk 41, each comprising a discriminator 34 and a selector 38 as described above.
  • terminals 4 are coupled to the selector 38 by wires 42 for carrying voice signals, and to the discriminator 34 by press-talk wires 7 for carrying press-talk signals.
  • the discriminator 34 controls the selector 38. When on or more of the incoming press-talk signals is active, the discriminator 34 selects one active press-talk signal, such as the one that became active first, and the selector 38 selects the corresponding voice signal.
  • the voice signal selected by the selector 38 is output on a signal line 43.
  • the press-talk signal selected by the discriminator 34 is output on a signal line 44.
  • the press-talk signal output on the signal line 44 is thus active when at least one of the received press-talk signals is active, and is inactive when all of the received press-talk signals are inactive.
  • the voice signal and press-talk signal output on the signal lines 43 and 44 from the slave press-talk trunk 41 are input to the the master press-talk trunk 40 together with the signals from the terminals 4 coupled to the master press-talk trunk 40.
  • the voice and press-talk signals output from the master press-talk trunk 40 may be input to a higher-order press-talk trunk not shown in the drawing.
  • the voice signal output by the highest-order press-talk trunk is input to a switching system and routed to all the terminals 4. This is indicated schematically in the drawing by signal lines 45 and 46 carrying the finally selected voice signal to all the terminal 4.
  • the cascading scheme results in a single press-talk signal and its corresponding voice signal being selected, even if the terminals are coupled to different press-talk trunks.
  • the master press-talk trunk 40 and slave press-talk trunk 41 therefore provide the same service as the single press-talk trunk in FIGS. 4 and 5, except that they can accommodate more terminals.
  • the cascaded press-talk trunks may all be installed in slots in the mainframe housing of the switching system. Cascading of press-talk trunks is also useful, however, when the terminals are grouped at two or more mutually distant locations. In this case a single press-talk trunk can be provided at each location, so that only a single press-talk signal line 44 and a single pair of voice signal lines 43 and 46 is required between locations, greatly reducing the amount of necessary wiring.
  • the master press-talk trunk 40 may be installed in a private branch exchange located in a main building while the slave press-talk trunk is located in an annex building, thereby reducing wiring between the main building and annex. Cascading of press-talk trunks in this way enables the 1 ⁇ N communication system to grow flexibly to meet expanding service requirements.
  • FIG. 7 shows a similar system in which the slave press-talk trunk 41 is coupled to the master press-talk trunk 40 by a wireless link comprising a pair of antennas 46 and 47. This scheme is particularly advantageous when the master press-talk trunk 40 and slave press-talk trunk 41 are widely separated.
  • the signal lines 43, 44, 45, and 46 in FIG. 6 may actually be multiplexed highways. When cascaded trunks are provided at different locations, line cards or fixed base stations may also be provided at these locations.
  • a space-division switch may be used instead of a time-division switch, and frequency-division multiplexing can be employed instead of time-division multiplexing.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Sub-Exchange Stations And Push- Button Telephones (AREA)
  • Mobile Radio Communication Systems (AREA)
US07/910,219 1991-07-10 1992-07-09 1×N communication system for private branch exchange Expired - Fee Related US5884162A (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP3-195044 1991-07-10
JP19504491A JPH0522190A (ja) 1991-07-10 1991-07-10 先取り判定システム
JP3-234312 1991-09-13
JP3234312A JP2743651B2 (ja) 1991-09-13 1991-09-13 １対ｎ通信方式

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US20050070221A1 (en) * 2003-09-30 2005-03-31 Upton Michael P. Vehicular repeater multi-unit system and method for allowing the first vehicular repeater unit on-scene to remain priority
US20050159144A1 (en) * 2002-03-22 2005-07-21 Hanz Hager Globally unique identification of groups of users in a communications system
US7127403B1 (en) 1999-09-13 2006-10-24 Microstrategy, Inc. System and method for personalizing an interactive voice broadcast of a voice service based on particulars of a request

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US5912882A (en) 1996-02-01 1999-06-15 Qualcomm Incorporated Method and apparatus for providing a private communication system in a public switched telephone network

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